Coupling assembly for carriage and actuator

ABSTRACT

A coupling device for connecting a carriage to an actuator includes a reciprocating and rotating key pin assembly supported by the actuator, and a slotted latch plate mounted to the carriage. The key pin assembly is normally biased by spring means towards the actuator. To couple the carriage and actuator, the spring bias is removed and the key pin assembly is advanced towards the latch plate, rotated and firmly engaged therewith. A rotary shaft supported by and movable with the actuator reciprocates and rotates the key pin assembly. When the actuator and carriage are stationary at home position, the shaft is linked to an engaging acceptor means located at a predetermined position in a stationary housing.

United States Patent Barnard et a1. 1 1 Dec. 10, 1974 [54] COUPLING ASSEMBLY FOR CARRIAGE 1,639,661 8/1927 -Newcomb 24/221 K AND ACTUATOR 2,138,229 1l/l938 Figge 403/349 2,811,765 11/1957 Mathews.... 24/221 K 1 Inventors: Cecil Percy Barnard, L05 Gates; 3,136,017 6/1964 PleZiOSl 24/221 Richard Burke Mulvany; Albert 3,431,537 3/1969 Klingenberg 24/221 K Daniel Rizzi, both of San Jose, all of Cahf- Primary Examiner-Bernard A. Gelak [73] Assignee: International Business Machines Attorney, Agent FirmNathan Kanman Corporation, Armonk, NY.

22 Filed: Nov. 6, 1972 ABSTRACT 2 APPL 303 743 A coupling device for connecting a carriage to an actuator includes a reciprocating and rotating key pin assembly supported by the actuator, and a slotted [52] US. Cl. 403/322, 24/211 K, 74/480 R, latch plate mounted to the carriage The key pin 74,20 sembly is normally biased by spring means towards the [51] It'll. C1 A441) 17/00 actuator To couplevthe carriage and actuator, the [58] Field of Search 24/221 K; 403/349, 353, spring bias is removed d h key in assembly is ad- 403/343, 322; 192/67 P; 74/480 20 vanced towards the latch plate, rotated and firmly engaged therewith. A rotary shaft supported by and [56] References cued movable with the actuator reciprocates and rotates the UNITED STATES PATENTS key pin assembly. When the actuator and carriage are 1,114,497 10/1914 MacDonald 403/343 ion ry at h m p i i n, h h f i link to n 1,203,606 11/1916 engaging acceptor means located at a predetermined 1,298,251 3/1919 position in a stationary housing. 1,597,198 8/1926 1,603,159 10/1926 9 Claims, 9 Drawing Figures PATENTEL LEE 1 [H974 3.853.415 sum 19F 54 PIC-3.1

PATENTELUEEWW 3353.415

SHEEI 30F 3 FIG.2A

COUPLING ASSEMBLY FOR CARRIAGE AND ACTUATOR CROSSED REFERENCE TO RELATED APPLICATION The coupling device of this invention is described in US. Pat. No. 3,786,454, entitled Magnetic Disk Storage Apparatus.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a mechanical coupling device and in particular to a novel assembly for coupling a carriage to an actuator.

2. Description of the Prior Art In presently known magnetic disk storage apparatus, linear actuators known as voice coil motors are mechanically connected to a carriage supporting a plurality of head arm assemblies, which are transported to selected data tracks of the disks. The bidirectional radial accessing movement of the head assemblies are exceedingly rapid, in the order of milliseconds, for each track access. Therefore, the mechanical connections and supports of the assembly of actuator, carriage and head arm must be suitable to maintain proper alignment and stability of operation. In those systems where the actuator, carriage and head arm assemblies are permanently mounted, except for replacement of defective parts, the problems of mechanical support and alignment are simplified. However, in a system where the actuator is a separate entity disposed in a housing, and the head arms and supporting carriage are part of a separable module which is independent of the housing, suitable connections must be made between the actuator and head carriage to avoid problems of mechanical separation, misalignment, or vibration. The carriage and arm assemblies must be rigidly coupled to the actuator to resist the separation forces induced by acceleration of the actuator, while the head arms remain properly aligned. In the case of a voice coil motor, the moving bobbin must be properly supported and aligned relative to the carriage to maintain a correct orientation of head arms to the storage disks.

SUMMARY OF THE INVENTION An object of this invention is to provide a novel and improved coupling device.

Another object of this invention is to provide a device for suitably coupling a carriage with an actuator.

Another object is to provide an assembly for coupling fast moving joined parts and an assembly that resists separation forces.

A further object is to provide a coupling assembly that affords suitable support and alignment of connectedmoving parts.

In a particular embodiment of this invention, an assembly is provided for coupling a head carriage structure contained in a disk module with the bobbin of a linear voice coil motor disposed in a stationary file housing. The coupling assembly employs a reciprocating and rotatable key pin element mounted to the voice coil motor. The key pin element is aligned to pass through a cooperating key slot of a latch plate supported by the disk module. An eccentric shaft is rotated so that the key pin is advanced and rotated into firm linkage with the slotted latch plate. Spring means, such as Belleville washers, urge the bobbin of the voice coil motor into close contact with the head carriage, and ensure that the coupled bobbin is fully supported and aligned relative to the carriage.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described in greater detail wit reference to the drawing in which:

FIG. I is a front view of part of a magnetic disk cartridge which is adapted to employ the coupling assembly of this invention;

FIG. 2 is a side sectional view of the novel coupling assembly made in accordance with this invention;

FIG. 2A is a side sectional view of the assembly of FIG. 2, in locked position;

FIG. 3 is a perspective view of an actuator sleeve, employed with the coupling assembly;

FIGS 4A and 4B are partial front views of the coupling assembly depicted in FIG. 2, in unlocked and locked positions respectively;

FIG. 5 is a top view of the assembly illustrated in FIG. 4A;

FIG. 6 is a front view of a coupler support and actuator; and

FIG. 7 is a top view of the assembly of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT The description in the aforementioned US. Pat. No. 3,786,454 of the apparatus employing the coupling assembly of the instant invention is hereby incorporated by reference. However, it should be understood that the present invention is not necessarily restricted to use in a magnetic disk file, but may be employed wherever there is a need to rigidly couple and align an actuating device with a carriage for conjoint bidirectional travel, particularly when there are rapid stops and starts, and reversal of direction occurring in milliseconds.

With reference to FIG. 1 in which a portion of a disk cartridge 10 is shown, a head carriage assembly 23 is mounted on inclined way surfaces 27 for bidirectional travel perpendicular to the plane defined by the drawing, and radially relative to magnetic disks 12, which are mounted to a hub within the cartridge. Attached to the' carriage assembly 23 is a mating latch plate 220 which encompasses a circular guide 229 formed with a pin clearance slot 232 and a top guide slot 234. The plate 220 with its guides and slots serves to engage the pin assembly that is provided with the actuator or voice coil bobbin 222, shown in FIG. 2.

In the sectional view of FIG. 2, the matching latch plate 220 and the circular guide 229, and top guide slot 234 are shown in alignment with the key pin assembly 244. The latch plate 220 provides piloting means to locate the bobbin assembly 222 of a voice coil motor (VCM) in vertical and horizontal position relative to the carriage 23. The latch plate 220 also provides a latching surface 224 at its carriage side, which provides a mating surface to mate with crosspin 226 in the bobbin coupling assembly. Latch plate circular pilot hole 228 engages with and initially locates coupling pin assembly 244. Latch plate circular guide 229 provides final alignment by engaging bobbin pilot 230. The en.- trance to the guide 229, the edge of the bobbin pilot 230, and the end of pin 244 are all tapered to aid in aligning the bobbin pilot to the latch, plate circular guide 229.

When the bobbin coupling is in its uncoupled position, and a cartridge is moved toward the bobbin for subsequent coupling, the crosspin 226 is in the position, as illustrated in FIG. 4A. Latch plate 220 includes the coupling pin clearance slot 232 (FIG. 1) to permit the coupling pin 226 to pass through the latch plate 220 on initial engagement of the latch plate with the bobbin assembly.

Rotational alignment of the bobbin assembly about the axis of access motion is provided by the interaction between latch plate top guide slot 234 and bobbin top pin 236. Parallel alignment between the access axis center line of the bobbin assembly and the access axis of the data module carriage is provided by mating pin surfaces which are carried in both the data module carriage and the bobbin. The face of two carriage lower pins 238 engage with the face of two bobbin bottom pins 240. The face of carriage top pin 242 engages with the face of bobbin top pin 236. The carriage mounted pins 238 and 242 are held in intimate contact with bobbin mounted pins 240 and 236, respectively, through the action of coupling pin assembly 244. The coupling pin assembly 244 is adapted to reciprocate along an axis parallel to the access axis of the bobbin, and is also suited to rotate bidirectionally 45. The pin assembly 244 is spring biased by Belleville spring washers 246 in a direction toward the VCM actuator 222. The spring washers 246 bear against an internal wall surface of the bobbin pilot assembly 230. A bias force from the washers 246 is applied through washer 248 to the pin assembly 244. The spring bias force provided by the Belleville spring washers 246 to mate the actuator 222 to the carriage 23 is selected to exceed the acceleration forces experienced by the carriage-actuator assembly during accessing operation.

If the crosspin 226 is inserted through the latch plate pin hole 228 and pin clearance slot 232 and is subsequently rotated 45, the crosspin 226 may no longer be drawn back through clearance slot 232. If the pin assembly 244 is then forced in a direction to the right, as illustrated in FIG. 2, relative to the pilot assembly 230, the action of the crosspin 226 in bearing against the latching surface 224 will tend to draw the bobbin assembly 222 into contact with the data module carriage assembly 23, and the two bobbin bottom pins 240 will be forced into contact with the two carriage bottom pins 238 while the bobbin top pin 236 will be forced into engagement with carriage top pin 242.

Longitudinal and rotational control of the pin assembly 244 to accomplish coupling and uncoupling is pro vided by the bobbin coupling assembly. The bobbin pilot assembly 230 is retained in the bobbin assembly 222 by snap ring 254. Rotational positioning of the bobbin pilot assembly is provided by locating pin 256, which engages a slot in the top of the bobbin pilot assembly 230.

When the coupling is in its engaged position and attached to the data module carriage assembly, as illustrated in FIG. 2A, washer 248 bears against a shoulder at the rear of the pin assembly 244. The longitudinal and rotational control of the pin assembly 244 is provided by means of an eccentric shaft 260 which accommodates a mounted needle bearing 262 and an actuator cam 264. The needle bearing provides longitudinal positioning of the pin assembly 244, and the actuator cam provides rotational positioning of the pin assembly 244.

FIG. 2 illustrates the coupling assembly in the uncoupled position. In this mode, needle bearing 262 bears against actuator sleeve 266. The actuator sleeve 266 incorporates a bore designed to accommodate the shouldered end of pin assembly 244. The depth of the bore in the actuator sleeve 266 is slightly longer than the length of the shouldered section of pin assembly 244. When the eccentric shaft 260 is rotated to bring the needle bearing 262 into engagement with the outer end of sleeve 266, the sleeve is moved to engage washer 248, thus removing the load of Belleville spring washers 246 from the pin assembly 244, and thereby minimizing the effort required to rotate the pin assembly. Further motion of the eccentric shaft and the needle bearing 262 causes the actuator sleeve 266 to move to the left, so that the end of the internal bore in sleeve 266 engages the end of pin assembly 244. Further motion of the needle bearing 262 will thus cause the pin assembly to move to the left.

Ball arm 252 engages ball slot 258 in actuator cam 264 in the uncoupled position, as in FIG. 4A. Clockwise rotation (when viewed from the top) of eccentric shaft 260 will cause the rotation of the actuator cam 264, and thus cause movement of ball arm 252 so as to rotate pin assembly 244 counterclockwise, as viewed in FIG. 2B. The eccentric shaft is designed for approximately ll2 of total rotation. As illustrated in FIGS. 2 and 4A, the bobbin and pin assembly is shown in its uncoupled position with the cross pin 226 at 45 to the vertical, and the pin assembly 244 extended outwardly from the bobbin assembly 222 by the action of eccentric shaft 260. In this position, actuator cam 264 bears against a stop-surface 267 with counterclockwise stop 265, illustrated in FIG. 5.

The eccentric shaft (when viewed from-the top in the uncoupled position) is positioned so that the high point of the eccentric relative to pin assembly 244 is approximately 20 counterclockwise from the access center line of the bobbin assembly. The thrust load supplied by the Belleville washers 246 tends to force the eccentric shaft to rotate in a counterclockwise direction, thus forcing counterclockwise stop 265 into intimate contact with stop surface 267.

During normal loading of the data module into the drive assembly, when the carriage 23 is brought into position to where the crosspin 226 is positioned behind surface 224 in cavity 292, the coupling is ready for actuation to couple to the carriage assembly. The eccentric shaft is rotated in a clockwise direction, when viewed from the top, to couple the bobbin assembly to the carriage assembly. During initial coupling rotation of the eccentric shaft 260, ball slot 258 tends to rotate pin assembly 244 through the action of ball arm 252. As the eccentric shaft 260 is rotated clockwise about 20, pin assembly 244 is extended slightly further from bobbin assembly 222, and crosspin 226 is rotated approximately 20 to a position about from the vertical. Additional clockwise motion of the eccentric shaft 260 completes the rotation of the crosspin to the horizontal position illustrated in FIG. 43.

At the position illustrated in FIG. 4B, the ball arm 252 has been rotated so that the ball is removed from ball slot 258, and lower cam surface 294 is positioned above the ball. Further coupling pin rotation is limited by the sidewall of ball arm clearance slot 296 (See FIG. 3). The eccentric shaft is free to turn after 45 of clockwise motion without causing further motion of the ball arm 252. This further eccentric motion allows the eccentric shaft to move needle bearing 262 to the left in FiG. 2 so that Belleville washers 246 may bias pin assembly 244 to cause crosspin 226 to contact surface 224. This contact under the load of Belleville washers 246 draws bobbin assembly 222 into intimate contact with carriage 23.

Detent spring 298 maintains actuator sleeve 266 in contact with needle bearing 262, and provides a bias force to force clockwise stop 300 into contact with stop surface 267 at the end of the coupling cycle. Slot 261 in eccentric shaft 260 permits manual operation of the coupler. Pin 302 engages key slot 304 in sleeve 266 to provide rotational position of the sleeve relative to pilot 230.

The coupling assembly described provides a simple coupling arrangement suitable to couple bobbin 222 to carriage 23 while maintaining careful alignment of bobbin to carriage. The coupling is suitable for manual or machine operation.

The Belleville washers 246 may be sized so as to provide axial coupling forces greater than the acceleration forces normally experienced by the bobbin/carriage system. The combination of axial and rotational motions of the pin assembly 244 permit the axial coupling load to be removed from the carriage 23 prior to pin rotation, thus minimizing coupling loads applied to the carriage, and minimizing the effort required to rotate the pin assembly. The crosspin 226 is moved axially away from and out of contact with latch plate surface 224 during pin rotation.

The bearing supported eccentric shaft 260 is selfcontained in the bobbin assembly, so that relatively high axial coupling forces, such as 50-100 lbs., can be utilized with only 3-4 inch lbs. of input torque required to operate the eccentric shaft.

The alignment of bobbin 222 to carriage 23, provided by the action of mating pins 238 and 242 to pins 240 and 236, along with the axial and rotational alignment provided by latch plate 220 and the mating force supplied by Belleville washers 246, assure that the coupled bobbin may be fully supported and aligned by carriage 23. The air gap of the voice coil motor in which the bobbin coil is suited to operate may be sized to accommodate bobbin alignment tolerances so that no VCM bobbin guides are required.

To disengage the coupling assembly from carriage 23 by machine operated means, the carriage is first positioned by the VCM actuator in its home position, so that eccentric shaft 260 is aligned coaxially with acceptor 86 (See FIG. 7). With the carriage at home position, the cable solenoid current is turned off, and acceptor element 86 is raised to rotate pivot lever 98 clockwise, as shown in FIG. 6, and to rotate latch release 102 counterclockwise and downward.

The carriage is latched and the coupling assembly has its eccentric shaft 260 engaged by acceptor 86, so that bayonet pin 88 (FIG. 4) is engaged by slot 85. Acceptor 86 is attached to coupling driver 82 by a flexible shaft 83. At the end of the upward motion of the acceptor and driver, key 96 is raised out of the slot in detent bearing 84 thus freeing the acceptor and driver for rotation under control of rack 120.

As the acceptor 86 is raised, it comes into contact with nesting plate 112, and raises first the end of the nesting plate closest to carriage 23, and then raises the opposite nesting plate end, so that the nesting plate is with surface 224. After approximately of eccentric shaft rotation, actuator cam 264 engages ball arm 252, 1

and pin assembly 244 is rotated clockwise, as viewed in FIGS. 4A and 4B, to the position shown in FIG. 4A, where crosspin 226 is aligned 45 to the vertical.

Rotation of the eccentric shaft 260 in the counterclockwise direction places the ends of bayonet pin 88 under nesting plate 112, thus positively locking the coupling assembly and bobbin 222 to the nesting plate.

As the acceptor is rotated counterclockwise, yoke cam surface 108 permits yoke 110 to be pulled in a direction away from the VCM by the action of tension springs. The yoke is pivotably supported by pivot pin 162 and pivot pin 163. Pivot pin 163 also provides a pivot for latch release lever 102.

The movement of yoke 110 away from the VCM carries nesting plate 112 into contact with bobbin retainer pin 91 (FIG. 2) so that the bobbin retainer pin is held in the fork 113 formed at the end of the nesting plate.

A second acceptor cam surface 115 on the acceptor 86 permits the acceptor and the bobbin 222 to move away from the VCM to assure proper mating of coupler and data module on the next data module loading cycle.

During the coupling mode, the machine operated sequence described above is reversed. The coupling assembly of this invention ensures that a secure, rigid connection and alignment is provided between a driver and driven element. Furthermore, when the driving motion is exceedingly rapid and subject to frequent reversals, the novel coupling assembly prevents separation and minimizes vibration of the moving parts. The invention is particularly useful in a magnetic disk file using a servo controlled voice coil motor actuator. In such systems, performance tends to suffer from excessive vibrations due to mechanical resonances. One cause of such vibrations is the tendency for the coupled voice coil motor and head carriage to separate. The present invention solves this problem by providing a simple low mass connection between the moving parts, so that they travel conjointly as a rigid integral unit.

Various features and advantages are obtainable with the coupling assembly of this invention. For example, the coupling assembly requires a minimum torque input to the eccentric shaft for operation, and requires relatively small forces to retain the carriage assembly in position on its guideway during coupling operation.

The combination of a needle bearing and actuator sleeve for unloading the spring bias force from the key assembly during rotation of the key pin assures minimum operating loads and minimum component wear.

The precision actuator coupling alignment and the precision sequential linear and rotational positioning applied to the key assembly under control of the camshaft insure minimum wear between the key pin and the latch plate during coupling and uncoupling operation.

By means of the disclosed arrangement, the coupling and uncoupling of an actuator and driven element are easily accomplished by external rotational drive means, such as the acceptor means described herein, that is fixed in a stationary housing, which may be a disk file by way of example. The stationary rotational drive means is adapted to engage and disengage from the coupling assembly of the key pin and slotted latch plate.

It is apparent that alternate embodiments are available. For example, the key pin and camshaft may be supported by the carriage, whereas the latch plate may be supported by the actuator.

What is claimed is:

1. An assembly for coupling a linear drive actuator assembly and a carriage assembly for conjoint linear travel, said actuator assembly comprising:

a key pin assembly having a crosspin formed at one end;

a pilot element disposed closely to said key pin assembly and facing said carriage assembly;

a first set of mating pins projecting from said actuator assembly towards said carriage assembly;

said carriage assembly comprising: a latch plate connected to one end of said carriage assembly, the latch plate having a mating surface including a pilot hole for engaging and initially locating said key pin assembly, and a guide formed with a clearance slot and a top guide slot for engaging said pilot element and for providing final alignment and engagement of said key pin assembly;

a second set of mating pins projecting from said carriage assembly for engaging said first set of mating pins to provide parallel alignment of said carriage assembly and said actuator assembly;

eccentric cam shaft means coupled to said actuator including a rotatable shaft, a cam formation on said shaft for linearly reciprocating said pin assembly relative to said carriage, a coupling pin coupled to and movable with said shaft and engaging said key pin assembly for rotating said pin assembly, so that said pin assembly and said latch plate may be joined in a stiff and fixed relationship;

spring means joined to said actuator assembly for biasing said pin assembly in a direction away from said latch plate and toward said actuator when said latch plate and pin assembly are joined, the bias force of said spring means being greater than the acceleration forces experienced by said actuator and carriage when joined for linear travel; and means connected to said eccentric shaft for unloading the spring bias force during rotation of said pin assembly relative to said latch plate.

2. An assembly as in claim 1, wherein said key pin as sembly reciprocates along an axis defined by the direction of its motion, and rotates bidirectionally about said axis for less than 3. An assembly as in claim 2, wherein said eccentric shaft controls the longitudinal motion of said pin assembly.

4. An assembly as in claim 3, further comprising a needle bearing mounted to said eccentric shaft that provides position control of the longitudinal motion, and an actuator cam mounted to said eccentric shaft that provides position control of the rotational motion of said pin assembly.

5. An assembly as in claim 4, including stop surfaces for limiting the movement of said actuator cam, thereby limiting the rotational motion of said pin assembly.

6. An assembly as in claim 1, wherein said shaft means serves to uncouple said pin assembly from said latch plate.

7. An assembly as in claim 1, wherein said drive actuator is a voice coil motor.

8. An assembly for coupling first and second movable parts for conjoint travel as an integral unit comprising:

slotted latch plate formed with said first part; reciprocable and rotatable key means formed with said second part for intimately engaging and separably couplable with said slotted latch plate; rotary eccentric shaft means supported by said second part and movable therewith and including a rotatable shaft, an eccentric on said shaft, and a coupling pin coupled to and movable with said shaft and engaging said key means for reciprocating and rotating said key means relative to said slotted latch plate to couple and uncouple said key means to ,said latch plate; and stationary means for accepting and engaging said rotary shaft means at a fixed point along the path of travel of said parts. 9. An assembly as in claim 8, wherein said stationary accepting and engaging means is adapted to move perpendicularly relative to said path of travel for engaging with and disengaging from said rotary shaft means.

l l k 

1. An assembly for coupling a linear drive actuator assembly and a carriage assembly for conjoint linear travel, said actuator assembly comprising: a key pin assembly having a crosspin formed at one end; a pilot element disposed closely to said key pin assembly and facing said carriage assembly; a first set of mating pins projecting from said actuator assembly towards said carriage assembly; said carriage assembly comprising: a latch plate connected to one end of said carriage assembly, the latch plate having a mating surface including a pilot hole for engaging and initially locating said key pin assembly, and a guide formed with a clearance slot and a top guide slot for engaging said pilot element and for providing final alignment and engagement of said key pin assembly; a second set of mating pins projecting from said carriage assembly for engaging said first set of mating pins to provide parallel alignment of said carriage assembly and said actuator assembly; eccentric cam shaft means coupled to said actuator including a rotatable shaft, a cam formation on said shaft for linearly reciprocating said pin assembly relative to said carriage, a coupling pin coupled to and movable with said shaft and engaging said key pin assembly for rotating said pin assembly, so that said pin assembly and said latch plate may be joined in a stiff and fixed relationship; spring means joined to said actuator assembly for biasing said pin assembly in a directiOn away from said latch plate and toward said actuator when said latch plate and pin assembly are joined, the bias force of said spring means being greater than the acceleration forces experienced by said actuator and carriage when joined for linear travel; and means connected to said eccentric shaft for unloading the spring bias force during rotation of said pin assembly relative to said latch plate.
 2. An assembly as in claim 1, wherein said key pin assembly reciprocates along an axis defined by the direction of its motion, and rotates bidirectionally about said axis for less than 180*.
 3. An assembly as in claim 2, wherein said eccentric shaft controls the longitudinal motion of said pin assembly.
 4. An assembly as in claim 3, further comprising a needle bearing mounted to said eccentric shaft that provides position control of the longitudinal motion, and an actuator cam mounted to said eccentric shaft that provides position control of the rotational motion of said pin assembly.
 5. An assembly as in claim 4, including stop surfaces for limiting the movement of said actuator cam, thereby limiting the rotational motion of said pin assembly.
 6. An assembly as in claim 1, wherein said shaft means serves to uncouple said pin assembly from said latch plate.
 7. An assembly as in claim 1, wherein said drive actuator is a voice coil motor.
 8. An assembly for coupling first and second movable parts for conjoint travel as an integral unit comprising: slotted latch plate formed with said first part; reciprocable and rotatable key means formed with said second part for intimately engaging and separably couplable with said slotted latch plate; rotary eccentric shaft means supported by said second part and movable therewith and including a rotatable shaft, an eccentric on said shaft, and a coupling pin coupled to and movable with said shaft and engaging said key means for reciprocating and rotating said key means relative to said slotted latch plate to couple and uncouple said key means to said latch plate; and stationary means for accepting and engaging said rotary shaft means at a fixed point along the path of travel of said parts.
 9. An assembly as in claim 8, wherein said stationary accepting and engaging means is adapted to move perpendicularly relative to said path of travel for engaging with and disengaging from said rotary shaft means. 